While classical X-ray imaging measures absorption of X-rays caused by an object, phase contrast imaging aims at a detection of a phase shift X-rays are subjected to when they pass through an object to be examined. For phase contrast imaging and/or dark-field imaging, a phase grating is placed behind the object to generate an interference pattern of intensity maxima and minima when the object is irradiated with (coherent) X-rays. Any phase shift in the X-ray waves that is introduced by the object causes some characteristic displacement in the interference pattern. Measuring these displacements therefore allows reconstructing the phase shift of the object. Employing such phase grating, in addition the generation of image data deriving from de-coherent X-ray small angle scattering is enabled, the latter type of imaging also being referred to as “dark-field imaging”.
EP 1 731 099 A1 discloses an X-ray interferometer arrangement comprising one phase grating and one amplitude grating. This interferometer can be used to obtain phase contrast images with a standard X-ray tube. Additionally, the interferometer may use a source consisting of an array of individual sub-sources. The array of sub-sources may be generated by placing an array of slits, i.e. an additional amplitude grating close to the source.
US 2010/0322380 A1 discloses hereto an X-ray detector that comprises an array of sensitive elements and at least two analyzer gratings disposed with different phase and/or periodicity in front of two different sensitive elements. The analyzer gratings with mutually different phases may be disposed in front the sensitive elements. The detector can be applied in an X-ray device for generating phase contrast images.
As a result, phase contrast imaging not only provides images showing the absorption of X-ray by the object under examination, but also additional images showing the phase shift of the X-ray beam by the object and the dark field of the object.
For phase contrast imaging, a setup with e.g. three different gratings is required. Two of those gratings are installed behind the patient and one of the two—the so-called analyzer grating—needs to be repositioned during imaging in order to sample the phase shift at various sampling positions. When performing phase contrast imaging, it is therefore assumed that the object is not moving. However, this is not an accurate assumption when imaging a moving object as e.g. parts of a coronary system or a pulmonary system.